Not applicable.
The present invention relates generally to mining bits adapted to have a longer life. More particularly, the present bits include modifications that enable them to withstand more wear than has heretofore been possible. Still more particularly, the present bits include a layer of protective material in the space between the bit threads and the shoulder of the bit.
The present application incorporates by reference in their entireties U.S. provisional application Ser. No. 60/025,858, filed Sep. 9, 1996, and application Ser. No. 08/925,700, filed Sep. 9, 1997 and now issued as U.S. Pat. No. 6,116,357, both entitled Improved Rock Drill Bit.
Drill bits are generally known, and fall into at least two categories. Drill bits used for drilling petroleum wells and drill bits used in the mining industry are both well known in the art. While these two types of bits superficially resemble each other, the parameters that affect the operation of each are completely different. Petroleum drill bits typically use a viscous, heavy drilling fluid (mud) to flush the cuttings from the vicinity of the bit and carry them out of the hole, whereas mining bits typically use compressed air to achieve the same purpose. Petroleum bits typically drill deep holes, on the order of thousands of feet, and each bit typically drills several hundreds or thousands of feet before being removed from the hole. In contrast, mining bits are used to drill relatively shallow holes, typically only 30-50 feet deep, and must be withdrawn from each shallow hole before being shifted to the next hole, resulting in severe backreaming wear. For these reasons, the factors that affect the design of mining bits are very different from those that affect the design of petroleum bits.
For instance, the viscosity and density of the drilling mud makes it possible to flush the cuttings from the hole even at relatively low fluid velocities. The air used to flush cuttings from mining holes, in contrast, is much less viscous and dense than drilling mud and therefore must maintain a rapid velocity in order to successfully remove the rock chips. The rapid flow of air across and around a rock bit greatly increases the erosive effect of the cuttings, particularly on the leading portions of the bit.
In addition, certain formations and certain drilling operations tend to cause extreme wear to the area adjacent to the cutting leg shoulder. For example, in some cases wear occurs between the let shoulder and the pin connection. Such wear is particularly a problem under poor cleaning conditions. In some instances, wear in this area under-cuts the leg shoulder and damages the pipe adapter that connects the bit to the drill string. If not checked, the wear will continue until the pin connection sealing face is destroyed on the bit or the adapter, or both.
Hence it is desirable to provide a mining bit that provides increased protection for the reservoir and its plug and opening. It is further desired to provide a bit that is capable of withstanding wear on its shoulders and legs during backreaming or as the bit is being withdrawn from a hole.
The present invention relates to drill bits that have been modified to withstand particular wear patterns that affect the portion of the bit body between the leg shoulder and the pin end of the bit. The present invention comprises applying a hard, wear resistant material to the area directly between the leg shoulder and the last machine section of the pin connection formed when the leg components are assembled. The hard, wear resistant material can be hardfacing such as welded on hard metal, flame spray applied hard metal, D-gun coating or, most preferably, sintered tungsten carbide inserts or sintered tungsten carbide inserts having a wear resistant surface, such as synthetic diamond or PCBN. The material can be applied in the form of a coating, as inserts, or as an annular piece.
In one embodiment of the invention, a drill bit comprises a bit body having a pin end, a cutting end and a longitudinal axis and including at least two legs extending from said cutting end, each of the legs including a leading side surface, a trailing side surface, and a shoulder, each of the legs further including a bearing and a cutter cone rotatably supported on the bearing. The bit body further includes a fluid flow system, including a flowway in the pin end, the flowway being in fluid communication with at least one exit port in the cutting end. The bit body further includes a neck between the shoulders and the pin end and a hard, wear-resistant material on at least a portion of the neck.
In another embodiment, a drill bit comprises a bit body having a pin end, a cutting end and a longitudinal bit axis and at least two legs extending from said cutting end, each of the legs including a bearing and rotatably supporting a cutter cone on the bearing. The bit body further includes a fluid flow system and a neck between the pin end and the legs. Each of the legs includes a leading side surface, a trailing side surface, and a center panel, at least one of said legs is asymmetric such that its trailing side surface is larger than its leading side surface. The fluid flow system includes a flowway in the pin end in fluid communication with at least one exit port in the cutting end, with the exit port being defined by a nozzle boss and disposed adjacent to one of said legs. The bit includes a hard, wear resistant material on at least a portion of the neck.
In still another embodiment, a drill bit comprises a bit body having a pin end, a cutting end, at least two legs extending from said cutting end, and a longitudinal bit axis and further including a fluid flow system, including a flowway in said pin end in fluid communication with at least one exit port in said cutting end, said exit port being defined by a nozzle boss and disposed adjacent one of said legs. Each of the legs includes a leading side surface, a trailing side surface, a shoulder and a center panel, and each of the legs is asymmetric such that more of the mass of the bit body lies between its trailing side surface and a plane through the bit axis and the center of its center panel than lies between its leading side surface and said plane. The bit body further includes a lubrication system in one of the legs, the lubrication system comprises a lubricant reservoir in fluid communication with the bearing, the reservoir comprises a cavity formed in the leg and having an opening in the trailing side surface one of the legs. The bit includes a hard, wear resistant material on at least a portion of the neck.